The present invention relates to a printing apparatus for printing marks such as letters and figures on printing webs such as papers.
There has been heretofore provided a so-called printer for printing letters, figures and the like on materials such as printing papers. In such a prior art printing machine, a printing drum is driven by a suitable motor to align in printing positions the letters and the like to be printed and then a hammer disposed on an opposite side to the printing drum is driven by solenoid means to hit the drum thereby completing the print on the printing papers positioned between the hammer and the drum.
However, the prior art printing apparatus requires the motor to rotate the printing drum and also the solenoid means having a large capacity enough to drive the hammer. Accordingly, the apparatus is disadvantageous in that the structure thereof is intricate with a large size and a large amount of an electrical power is required to drive the solenoid means.
In order to eliminate such defects, an improved printing apparatus has been proposed in U.S. patent application Ser. No. 147,655 filed on May 7, 1980 and entitled "Printing Apparatus." In this printing apparatus, a printing drum to which a rotational torque from a rotational drive means is normally applied is arranged so as to face to a printing web, and a lever swingable against the printing web suitably supported by a roller rotatably carries the printing drum, and a forcible stopping means serves to prevent the rotation of the printing drum around its own axis whereby the lever can be rotated toward the printing web. According to such a printing apparatus, it is essentially possible to control both the rotation of the printing drum and the printing operation by a single motor. The printing apparatus is, therefore, simple in construction and small in size. Moreover, a small capacity is required for the solenoid means since the solenoid means only serves to rotate a stop lever at a small angle. For this reason, energy consumption may be reduced.
However, such a printing apparatus has the following disadvantages due to the fact that the forcible stopping means includes a ratchet wheel provided to the printing drum and the ratchet teeth ride over the projected stop lever to thereby carry out the printing operation. That is, it is difficult to effectively apply the generated drive force in the printing web direction during the ride-over of the ratchet teeth.
More specifically, the load applied to the motor is increased, which shortens the service life of the motor. Since a large amount of brake force is required for the forcible stopping means, the mechanical strength of the forcible stopping means must be enhanced, which results in the engagement of the apparatus. Also, since the stroke of the printing drum cannot be elongated beyond the ratchet tooth height, it is difficult to adjust the impact timing of the printing drum against the printing web. Furthermore, since the printing drum is rotated around its own axis to carry out the printing, the printing displacement tends to take place. It is also impossible to enhance the printing speed more than a predetermined value. Therefore, a main object of the present invention is to overcome the above-noted defects.